Problem: Kevin is 30 years older than Umaima. Twelve years ago, Kevin was 4 times as old as Umaima. How old is Umaima now?
Answer: We can use the given information to write down two equations that describe the ages of Kevin and Umaima. Let Kevin's current age be $k$ and Umaima's current age be $u$ The information in the first sentence can be expressed in the following equation: $k = u + 30$ Twelve years ago, Kevin was $k - 12$ years old, and Umaima was $u - 12$ years old. The information in the second sentence can be expressed in the following equation: $k - 12 = 4(u - 12)$ Now we have two independent equations, and we can solve for our two unknowns. Because we are looking for $u$ , it might be easiest to use our first equation for $k$ and substitute it into our second equation. Our first equation is: $k = u + 30$ . Substituting this into our second equation, we get the equation: $(u + 30)$ $-$ $12 = 4(u - 12)$ which combines the information about $u$ from both of our original equations. Simplifying both sides of this equation, we get: $u + 18 = 4 u - 48$ Solving for $u$ , we get: $3 u = 66$ $u = 22$.